The Yunnan–Kweichow Plateau serves as a critical ecological security barrier in southwest China. The region has witnessed substantial transformations in land use patterns due to rapid urban expansion, economic development, and population growth. These changes have significantly impacted the structure and services of regional ecosystems. Conducting a quantitative analysis of the influence of land-use changes on ecosystem service value (ESV) proves to be invaluable for guiding regional land planning and environmental conservation efforts. Utilizing land use data, we calculated ESV variations linked to dynamic land-use changes spanning the period from 1980 to 2020. This comprehensive study delved into the spatiotemporal fluctuations and regional disparities in ESV. To enhance the reliability of our evaluation, we applied a regional coefficient to adjust the equivalent factor of ecosystem service value. Over the 40 years, the total ESV exhibited a decrease from USD 122,215.03 million to USD 121,838.82 million. Notably, water supply experienced the most significant decline, while hydrological regulation witnessed the largest increase. The continuous decline in water supply service capacity raises concerns about exacerbating water resource shortages in the region. Spatially, the ESVs in the study region primarily concentrated within the medium-low to medium-high value range. However, except for regions with medium values, the area of other level regions is expanding, and is particularly evident in the increase in low-value regions. The reduction of forestland, grassland, and cultivated land, coupled with the expansion of built-up land, emerged as the primary contributors to the overall ESV decrease. In particular, the negative ecological contribution rate of built-up land reached 37.97%, and the ESV decreased by USD 866.64 million, underscoring that the expansion of water bodies could not compensate for this loss. The study highlights the increasing sensitivity of ESV to land-use changes in the region. As a response, there is a pressing need for managers to reinforce the implementation of ecological engineering and engage in rational planning for production, living, and ecological spaces. This research serves as a crucial reference for establishing an ecological security pattern system and fostering the sustainable development and utilization of land resources in the region.

The high-intensity partial pressure of CO₂ (pCO₂) in karst underground rivers rapidly releases in open-flow sections. This is an important process affecting the global karst carbon cycle. This study focuses on the diurnal variation patterns and driving factors of CO₂ exchange flux at the water–air interface in the open-flow sections of typical karst underground rivers in southwestern China. The inorganic carbon in water and water–air interface exchange fluxes are observed. Three representative survey stations, i.e., the outlet of the underground river (Q1), the river sections without submerged plants (H1), and the river sections with submerged plants (H2), are selected to study the CO₂ exchange process and its influencing factors. The results show that the CO₂ release flux at Q1 exhibits high pressure in the daytime and low pressure in the nighttime, while H1 and H2 exhibit the opposite pattern. The photosynthesis of submerged plants significantly inhibits the carbon release flux of the river, and in the river sections where submerged plants are distributed, their biological effects have inhibited approximately 0.131 Tg C/yr of carbon emissions. This study emphasizes the significant contribution of submerged plants in restraining the release of CO₂, thereby promoting carbon sequestration and storage in karst water systems.

The high-intensity pCO₂ in karst underground river water is rapidly released or absorbed by aquatic organisms in open flow sections and is an important factor affecting the karst carbon cycle. This article takes a typical karst underground river basin in southwestern China as the research object. By observing the water carbon and water‒air interface exchange fluxes at the outlet of the underground river (Q1), the river section without submerged plants (H1), and the river section with submerged plants (H2), the diurnal variation pattern and driving factors of CO₂ flux at the water‒air interface in the karst area were evaluated, and the transformation process of water carbon and the source sink changes in water carbon in the open-flow section were explored. The results show that CO₂ flux and pCO₂ in the study area exhibit significant spatial differences, with the outlet of the underground river having the highest values. DO is found to be a key controlling factor affecting changes in CO₂ flux. The metabolism of submerged plants has a regulatory role on the change in CO₂ flux, forming a carbon sink in the river section with submerged plants. Therefore, this study helps to understand the diurnal variation in carbon exchange fluxes at the water‒air interface in the open flow section of karst underground rivers and emphasizes the variation pattern of CO₂ fluxes from source to sink in the open flow section, providing an effective way to promote carbon sequestration and sink enhancement in karst water bodies.

Despite extensive research on soil organic carbon in karst regions, the synergistic changes in multiple carbon fractions and their stabilization mechanisms across a complete rocky desertification gradient remain poorly understood. To clarify how soil carbon pools and their drivers change during karst rocky desertification, we selected Kaiyuan City, Yunnan Province, China, as the study area. Total carbon (TC), soil organic carbon (SOC), and their related fractions, including particulate organic carbon (POC), mineral-associated organic carbon (MAOC), iron-bound organic carbon (Fe-OC), calcium-bound organic carbon (Ca-OC), and soil carbon isotopic composition (δ¹³C), were analyzed under different degrees of rocky desertification. SOC and TC followed a nonlinear pattern: increasing from no to potential desertification, decreasing at light and moderate stages, and rising again at the severe stage, indicating a phased response rather than a monotonic decline. POC was lowest under no rocky desertification and increased significantly after desertification occurred, reaching its maximum at the severe stage. MAOC peaked at the potential stage. With increasing rocky desertification severity, POC/SOC increased from no to moderate stages and then slightly decreased, whereas MAOC/SOC generally decreased. Fe-OC and Ca-OC were lowest under no desertification and increased after desertification occurred, pointing to enhanced mineral protection. Soil δ¹³C values under moderate and severe desertification were higher than under no, potential, and light desertification, implying intensified decomposition and a relative increase in C₄ plants. Mean weight diameter (MWD) and geometric mean diameter (GMD) did not differ significantly among rocky desertification stages (p > 0.05). In contrast, fractal dimension (FD) differed significantly only between the light and moderate stages (p < 0.05). Correlation and redundancy analyses showed that soil water content, bulk density, and porosity were the key factors driving variation in SOC and its fractions. These findings provide both a theoretical basis and practical guidance for soil restoration and ecological management in karst faulted basins affected by rocky desertification.